1. Field of the Invention
This invention relates to a zoom lens, and more particularly to a zoom lens which is capable of 2X or higher zooming ratio, covers a 65.degree. field and which requires as few as three lens components.
2. Description of Prior Art
Because of the desire to reduce the size, weight and cost of photographic cameras, efforts are being made to reduce the size, weight and cost of the optical systems for use in such cameras, and particularly the taking lens used to expose photographic film or other light-sensitive materials such as for use in 35 mm cameras (135 mm format).
Most two-unit zoom lens systems having a front negative and a rear positive configuration require that the front unit comprise at least one positive and one negative lens component and that a rear lens unit comprise a plurality of lens elements arranged in a triplet or triplet derivative configuration. We define herein a triplet derivative configuration as a configuration of lens elements consisting of a negative power lens component or element situated in an air space and surrounded by two or more positive lens elements. Examples of such configurations are disclosed in U.S. Pat. Nos. 4,993,814, 4,560,253, 4,400,064, 4,195,912, 4,074,931 and 4,118,108. As shown in the prior art, this configuration typically comprises six to eight lens components.
U.S. Pat. No. 4,993,814 also shows a simplification of the above design in that the positive lens element can be eliminated from the front group. The rear group was also simplified into a form of classical triplet, i.e., three air spaced lens element arranged in a plus, minus, plus configuration. The result is a front group consisting of a single negative element and a rear group consisting of only three air spaced elements. U.S. Pat. No. 4,999,007 also shows the above improvement, but in addition discloses an alternative configuration (see FIGS. 6, 7 and 9 of U.S. Pat. No. 4,999,007)--a lens system comprised of at least three lens components arranged into three lens units. The first two units move independently during zooming and each comprises a single lens element. The rear or third unit is stationary. However, further need for lens system simplification still exists.